1. Field of the Invention
The present invention relates to a high-speed optical recording method and apparatus where marks can be erased at an optimal erasing rate even at high speed.
2. Description of the Related Art
Generally, optical recording/reproducing apparatuses use a single semiconductor laser to record a mark on an optical disc, and record an information signal on the optical disc by driving the semiconductor laser in a multi-pulse form according to the length of the mark to be recorded. For example, a phase change optical disc capable of repetitively recording is used as the optical disc, so that the recording of the mark is performed while erasing an existing mark previously recorded on the optical disc. Thus, an erasing signal is located on a period between recording signals, which corresponds to a length of the mark to be recorded.
Because the recording density is on an increasing trend and a high data transfer rate is demanding, a high recording rate is required and a fast erasing must be possible in order to obtain a high recording rate. However, because recording and erasing on the optical disc are generally performed by moving a single light spot emitted from the semiconductor laser and focused by an objective lens along a track, the light spot must move slower when erasing than when recording in order to achieve a desired erasing ratio, which is proportional to the time of radiation of the light spot. Hence, it is difficult to achieve fast erasing that satisfies a required high recording speed.
Fast erasing may be achieved by changing the structure of the optical disc. In existing systems, a crystallization accelerating layer is stacked on the upper and lower surfaces of a recording layer of the optical disc has been proposed in order to improve the erasing ratio of a recorded mark. However, the thus-structured optical disc requires an increase in the number of stacks, thereby creating disadvantages in terms of yield and mass, production. Also, while crystallization is achieved well due to the existence of a crystallization accelerating layer, an adjacent track in the optical disc is affected by the crystallization during recording. Specifically, the mark recorded on the adjacent track is erased.